Polychlorinated biphenyls (PCBs) and the DDT family are toxic, widespread hydrocarbons that are poorly understood in terms of their toxicity for human beings. In addition to their direct toxicity, both of these chemicals pass from mother to child through the placenta and by contaminating breast milk. This project includes a study of subjects exposed to low levels of these compounds in the US and two studies of subjects exposed to higher doses in Taiwan. The Breast Milk and Formula study is a birth cohort follow up study of 856 North Carolina children. PCBs and DDE (the stored metabolite of DDT) are measured in breast milk and the children are followed medically over time. Most of the children have completed 5 years of observation and are now followed only by a birthday card registry. This study has shown that more than 90% of NC breast milk samples have PCBs and DDE detectable; levels of PCBs are as high in NC as in areas thought to have special exposures. Levels of both PCBs and DDE decline over the course of lactation, and levels are higher in first than in subsequent lactations. Children exposed to higher levels of DDE and PCBs transplacentally are more likely to have mild degrees of neurological impairment at birth. Women with higher levels of DDE breast feed for shorter lengths of time. An epidemic of 2000 cases of PCB poisoning occurred in Taiwan in 1979. Rice oil was accidentally contaminated during manufacture. We did a survey of 108 children who were born to mothers who were poisoned, 40 of their older siblings, and 106 controls. All children received a physical examination and the mothers answered a questionnaire about their children's health. Another study of this outbreak used a modification of an assay for sister chromatid exchanges to evaluate the potential for long term, subtle genetic damage, as well as assays for cellular immune function.